In this section, you will learn how to use persisted operations in GraphQL with Hot Chocolate.

Persisted operations allow us to pre-register all required operations of our clients. This can be done by extracting the operations of our client applications at build time and placing them in the server's operation document storage.

Extracting operations is supported by client libraries like Relay and in the case of Strawberry Shake we do not have to do any additional work.

How it works

• All operations that our client(s) will execute are extracted during their build process. Individual operation documents are hashed to generate a unique identifier for each operation.
• Before our server is deployed, the extracted operation documents are placed in the server's operation document storage.
• After the server has been deployed, clients can execute persisted operations, by specifying the operation ID (hash) in their requests.
• If Hot Chocolate can find an operation that matches the specified hash in the operation document storage it will execute it and return the result to the client.

Note: There are also automatic persisted operations, which allow clients to persist operation documents at runtime. They might be a better fit, if our API is used by many clients with different requirements.

Benefits

There are two main benefits to using persisted operations:

Performance

• Only a hash and optionally variables need to be sent to the server, reducing network traffic.
• Operations no longer need to be embedded into the client code, reducing the bundle size in the case of websites.
• Hot Chocolate can optimize the execution of persisted operations, as they will always be the same.

Security

The server can be tweaked to only execute persisted operations and refuse any other operation provided by a client. This gets rid of a whole suite of potential attack vectors, since malicious actors can no longer craft and execute harmful operations against your GraphQL server.

Usage

First we have to instruct our server to handle persisted operations. We can do so by calling UsePersistedOperationPipeline() on the IRequestExecutorBuilder.

public void ConfigureServices(IServiceCollection services)
{
    services
        .AddGraphQLServer()
        .AddQueryType<Query>()
        .UsePersistedOperationPipeline();
}

Production Ready Persisted Operations

In transitioning your persisted operation setup to production, simply setting up a persisted operation file isn't sufficient for a robust production environment. A key aspect of managing persisted operations at scale involves version management and ensuring compatibility with your GraphQL schema. The client registry is your go-to resource for this purpose.

The client registry simplifies the management of your GraphQL clients. It allows for the storage and retrieval of persisted operation documents through their hashes but also ensures that these operations are validated against the current schema on publish, preventing runtime errors due to schema-operation mismatches. Additionally, it supports versioning of your clients, allowing seamless updates and maintenance without disrupting existing operations.

Check out the client registry documentation for more information.

Other Storage mechanisms

Hot Chocolate supports two operation document storages for regular persisted operations.

Filesystem

To load persisted operation documents from the filesystem, we have to add the following package.

dotnet add package HotChocolate.PersistedOperations.FileSystem

After this we need to specify where the persisted operation documents are located. The argument of AddFileSystemOperationDocumentStorage() specifies the directory in which the operation documents are stored.

public void ConfigureServices(IServiceCollection services)
{
    services
        .AddGraphQLServer()
        .AddQueryType<Query>()
        .UsePersistedOperationPipeline()
        .AddFileSystemOperationDocumentStorage("./persisted_operations");
}

When presented with an operation document hash, Hot Chocolate will now check the specified folder for a file in the following format: {Hash}.graphql.

Example: 0c95d31ca29272475bf837f944f4e513.graphql

This file is expected to contain the operation document that the hash was generated from.

Redis

To load persisted operation documents from Redis, we have to add the following package.

dotnet add package HotChocolate.PersistedOperations.Redis

After this we need to specify where the persisted operation documents are located. Using AddRedisOperationDocumentStorage() we can point to a specific Redis database in which the operation documents are stored.

public void ConfigureServices(IServiceCollection services)
{
    services
        .AddGraphQLServer()
        .AddQueryType<Query>()
        .UsePersistedOperationPipeline()
        .AddRedisOperationDocumentStorage(services =>
            ConnectionMultiplexer.Connect("host:port").GetDatabase());
}

Keys in the specified Redis database are expected to be operation IDs (hashes) and contain the actual operation document as the value.

Hashing algorithms

Per default Hot Chocolate uses the MD5 hashing algorithm, but we can override this default by specifying a DocumentHashProvider.

public void ConfigureServices(IServiceCollection services)
{
    services
        // choose one of the following providers
        .AddMD5DocumentHashProvider()
        .AddSha256DocumentHashProvider()
        .AddSha1DocumentHashProvider()

        // GraphQL server configuration
        .AddGraphQLServer()
        .AddQueryType<Query>()
        .UsePersistedOperationPipeline()
        .AddFileSystemOperationDocumentStorage("./persisted_operations");
}

We can also configure how these hashes are encoded, by specifying a HashFormat as argument:

AddSha256DocumentHashProvider(HashFormat.Hex)
AddSha256DocumentHashProvider(HashFormat.Base64)

Note: Relay uses the MD5 hashing algorithm - no additional Hot Chocolate configuration is required.

Blocking regular operations

If you want to disallow any dynamic operations, you can enable OnlyAllowPersistedDocuments:

builder.Services
    .AddGraphQLServer()
    // Omitted for brevity
    .ModifyRequestOptions(
        options => options
            .PersistedOperations
            .OnlyAllowPersistedDocuments = true);

This will block any dynamic operations that do not contain the id of a persisted operation.

You might still want to allow the execution of dynamic operations in certain circumstances. You can override the OnlyAllowPersistedDocuments rule on a per-request basis, using the AllowNonPersistedOperation method on the OperationRequestBuilder. Simply implement a custom IHttpRequestInterceptor and call AllowNonPersistedOperation if a certain condition is met:

builder.Services
    .AddGraphQLServer()
    // Omitted for brevity
    .AddHttpRequestInterceptor<CustomHttpRequestInterceptor>()
    .ModifyRequestOptions(
        options => options
            .PersistedOperations
            .OnlyAllowPersistedDocuments = true);

public class CustomHttpRequestInterceptor
    : DefaultHttpRequestInterceptor
{
    public override ValueTask OnCreateAsync(
        HttpContext context,
        IRequestExecutor requestExecutor,
        OperationRequestBuilder requestBuilder,
        CancellationToken cancellationToken)
    {
        if (context.Request.Headers.ContainsKey("X-Developer"))
        {
            requestBuilder.AllowNonPersistedOperation();
        }

        return base.OnCreateAsync(
            context,
            requestExecutor,
            requestBuilder,
            cancellationToken);
    }
}

In the above example we would allow requests containing the X-Developer header to execute dynamic operations. This isn't particularly secure, but in your production application you could replace this check with an authorization policy, an API key or whatever fits your requirement.

Client expectations

A client is expected to send an id field containing the operation document hash instead of a query field.

HTTP POST

{
  "id": "0c95d31ca29272475bf837f944f4e513",
  "variables": {
    // ...
  }
}

Note: Relay's persisted queries documentation uses doc_id instead of id, be sure to change it to id.